Closed deck engine blocks refer to engine blocks wherein an area between an outer surface of a cylinder bore and an outer surface of a space defining a water jacket that surrounds the outer surface of the cylinder bore are bridged or connected with supporting material to enhance the stability of the cylinder bore during combustion. In contrast, open deck engine blocks refer to engine blocks where the cylinder bores are not supported.
U.S. Pat. No. 8,820,389; which is hereby incorporated herein in entirety by reference; discloses a method for high pressure die casting of an engine block assembly having at least one cast in place cylinder bore in the engine block, and a closed head deck surface. In the disclosed method, an outer upper surface of at least one cast in place cylinder bore is surrounded with a salt core to create a composite core. The salt core defines the water jacket. The composite core is placed into a high pressure die casting mold for a closed deck engine block and an engine block alloy is injected into the mold. The cast engine block and composite core are removed from the high pressure die casting mold as a single engine block assembly and cooled. The salt portion of the composite core is dissolved. In certain embodiments, the salt core defines orifices in the closed head deck. The drawback of this method is that it requires that the cylinder bores be pre-cast and then cast into place using the composite core method. Another drawback is that there is difficulty in removing the large amount of salt used for the salt core.
U.S. Pat. No. 4,875,517 entitled “Method of producing salt cores for use in die casting” and also incorporated herein in entirety by reference, describes a method of producing salt cores for use in traditional die casting (not high pressure) by means of an evaporative foam pattern held in place with sand.
U.S. Pat. No. 7,013,948 entitled “Disintegrative Core for use in use in Die Casting of Metallic Components” and incorporated herein in entirety by reference details the manufacture of salt cores with a vent opening to allow gases to pass inward through the body of the salt core and away from the salt core's outer surface. This salt core technology is used in traditional die casting to produce engine blocks and engine head decks.
However, the high pressure die casting method traditionally has been limited. The use of sand cores made from sand molded within a geometric cavity and held together with an organic binder remain confined to use in low pressure and sand casting methods due to the fragile nature of the core body. Likewise, salt cores are often too fragile to withstand the influx of pressurized molten metal while retaining their necessary shape. Particularly, the intricacies of the head decks of engine blocks are problematic to cast with high pressure die casting because of tight tolerances between cylinder bores and the water cooling jackets surrounding the cylinder bores, which generally require sand or salt core technology. Such engine head decks are even more problematic when the casting requires a closed deck where only a selected area is open to the water cooling jacket area. Closed deck engine blocks are characterized by a water jacket that is substantially closed at the top portion of the engine block, with the exception of any relatively small passages that may be present to facilitate core support, transmit gas during casting, or for creating cooling water passages to the cylinder head of the engine assembly. This closed deck design provides increased cylinder bore rigidity by adding support to the cylinder bore by bridging the cylinder bore to a water jacket wall with an integrated casting component, i.e. closing the head deck.
Thus, the water cooling passages of open deck high pressure die cast aluminum engine blocks are currently produced such that the combustion cylinders are formed using metallic cores on the inner diameter and outer diameter that leaves the cylinder walls free-standing, i.e. an open deck. This condition does not provide good structural strength to the cylinder in operation due to the high levels of stress caused during combustion, compression, and thermal stresses during engine operation. Specifically, the lack of head deck bridges in a high pressure die cast block does not provide solid support of the cylinder in operation. Moreover, the water jackets of open deck type engine blocks have to be sealed during the cylinder head assembly. This sealing process is generally very fault-prone and involved. Because of these drawbacks, large displacement aluminum engine blocks having high mechanical and thermal stress loads have not typically been produced using high pressure die casting.
While a closed deck engine block affords significantly greater load support, the prior art was limited in its ability to produce the optimum water jacket cooling passage geometry combined with the desired structural rigidity of a closed deck engine block. In that regard, U.S. Pat. No. 6,478,073 is also directed to a “Composite Core for Casting Metallic Objects” The patent details the manufacture of a salt core using a metallic arbor to provide structural support. These cores are produced using high pressure die casting and molten salt surrounding an aluminum arbor. The rigid nature of the internal arbor provides structural stability necessary for the forces of molten metal put upon the core during high pressure casting processes. The salt/aluminum core are subsequently placed in a high pressure die casting die and an aluminum engine “head” is cast around it. After casting, the salt core is dissolved by flushing with water and the aluminum arbor is extracted, leaving a cored cavity in place of the salt core. However, the arbor support is inadequate for the casting of closed deck engine blocks because the nature of the closed deck prevents the arbor from being removed. Conversely, without using an arbor as described in the '073 patent, a salt core is too fragile to withstand the high pressure die casting forces.
One closed head deck solution is Ford Global Technologies, LLC U.S. Pat. No. 6,886,505 entitled “Cylinder block and die-casting method for producing same”. This patent details the production of high pressure die cast engine blocks with a closed deck water jacket by means of die core opening on the exterior surfaces of the engine block casting. However, the water jacket is open towards the engine block core requiring covers to be added to seal the water jacket with bolts. Thus, the water jacket is not fully closed when cast, nor is the engine block a unitary casting. This non-unitary casting and cover requirement adds additional steps to the manufacturing process and creates a risk of leaks that would not be present should the closed deck water jackets be a unitary casting.
Applicants are also aware of prototype cores and engine blocks produced by Buhler Die Casting Machinery of Germany and VW Automotive of Germany. Buhler developed a salt core for placement in a high pressure die cast die to form simple shape cored passages for water jacket cooling and a fully closed head deck. The cores are placed into the die and located with through-wall hole details that extend into the die. The engine block and cylinders are then cast using a hypereutectic aluminum silicon alloy. The inside of the cylinder wall is formed with a retractable, cylindrical, water-cooled tool steel core. The outer wall of the cylinder is formed by the salt core. After casting, the salt core is washed from the casting leaving the water cooling jacket passage open under the closed head deck of the block. However, since the salt core is fragile and unsupported, the prototypes have been relatively unsuccessful in that the salt cores fail during casting creating an unacceptable number of blocks that must be scrapped.
Accordingly, prior to the present invention, tooling and manufacturing trade-off decisions based the design stresses of the engine and the capability of the existing technology. Manufacturers were limited in their ability to produce the optimum water jacket cooling passage geometry while maintaining the desired structural rigidity of a closed deck engine block, particularly using the more efficient high pressure die casting method.